This application is related to Japanese Patent Application No. 2000-340654 filed on Nov. 8, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a vapor-compression refrigerant cycle for a vehicle, having a compressor which sucks and compresses refrigerant using a power from a driving source (e.g., engine) for travelling the vehicle.
2. Description of Related Art
In a conventional vehicle air conditioner with a vapor-compression refrigerant cycle, generally, a part of power of an engine for travelling the vehicle is supplied to a compressor through an electromagnetic clutch. Therefore, in an engine having a relatively small displacement, when the vehicle accelerates or is traveling on an uphill road, driveability of the vehicle is deteriorated. Here, the driveability means a vehicle speed change relative to an operation amount of an acceleration pedal.
For example, in JP-B2-3-58927, an acceleration state is determined from a throttle opening degree, and an electromagnetic clutch is turned off so that a power transmission from an engine to a compressor is interrupted when the throttle opening degree of the vehicle is larger than a predetermined degree. However, in this case, the on/off operation of the electromagnetic clutch is repeatedly performed because the throttle opening degree of the vehicle is changed even when the vehicle is travelling with a fixed speed. Accordingly, it is difficult to improve the driveability in the vehicle.
In view of the foregoing problems, it is an object of the present invention to provide a refrigerant cycle for a vehicle having a compressor operated by power from a driving source for travelling the vehicle, which improves driveability in the vehicle.
According to the present invention, in a refrigerant cycle for a vehicle being travelled by a driving source, a compressor is operated by a power from the driving source to suck and compress refrigerant, a load detecting unit is disposed to detect load of the driving source, a vehicle speed detecting unit is disposed for detecting a vehicle speed, and a power reducing unit reduces a consumed power consumed in the compressor when the load detected by the load detecting unit is equal to or larger than a first threshold value. In the refrigerant cycle, a control unit for controlling operation of the compressor sets the first threshold value in such a manner that an increase rate of the first threshold value relative to the vehicle speed becomes larger as the vehicle speed becomes larger. Accordingly, driveability of the vehicle can be improved.
Preferably, the first threshold value is set based. on the vehicle speed detected by the vehicle speed detecting unit to be approximately equal to a value obtained by multiplying a load of the driving source, determined based on the vehicle speed, and a predetermined number together. In this case, the driveability of the vehicle can be further improved.
Alternatively, the first threshold value is set to be larger as the vehicle speed detected by the vehicle speed detecting unit becomes larger, in such a manner that a relationship between the first threshold value and the vehicle speed approximates to a secondary function. In a normal throttle opening-degree curved line Lo, showing a relationship between the vehicle speed and the throttle opening degree when the vehicle is travelling on a flat road in a state without an air flow, a relationship between the first threshold value and the vehicle speed has the secondary function. Therefore, the driveability in the vehicle can be further improved.
Further, the control unit includes power-returning means, the power-returning means stops power-reducing operation of the power reducing unit so that power consumed in the compressor is returned when the load detected by the load detecting unit is equal to or smaller than a second threshold value smaller than the first threshold value, and the control unit sets the second threshold value in such a manner that a difference between the first threshold value and the second threshold value becomes larger as the vehicle speed detected by the vehicle speed detecting unit becomes larger. Therefore, consumed power consumed in the compressor can be readily returned while the driveability of the vehicle is improved.
More preferably, the control unit sets a prohibition area when the vehicle speed is larger than a predetermined speed, and the control unit prohibits power-reducing operation of the power reducing unit in the prohibition area. Therefore, when the vehicle is travelling. in a high speed higher than the predetermined speed, hunting in the compressor can be prevented.